1999 GMC Yukon 94000k 350

I am getting a misfire code on #5 cyl, The rep. said to rebuild or
replace engine.
Was a little reluctant on doing that so I ask for a compression test to

be done.  They said that would be $120 so I said OK..  No. 5 was 140lbs

and adjoining cyls was 150.  I asked what the dif was between the wet
and dry and he didnt know what I was talking about.  After several
calls he got with the mech. and he said they done wet/dry on #5 with no

diff. also a leak down test showed it was bad rings.  With these
responses I dont know how good of a job was done on the tests.  I
replaced the plugs and the light goes off for a while and then on for a

while.  My biggest question is how to rule out other possible problems
before moving on to the bad rings.  Such items as EGR valve, bad
ignition, fuel, etc.